Method of integrally sealing an electronchemical fuel cell fluid distribution layer

ABSTRACT

A fuel cell comprises a pair of separator plates and a pair of fluid distribution layers interposed between the separator plates. At least one of the fluid distribution layers comprises a sealing region and an electrically conductive, fluid permeable active region, and a polymeric material extending into each of the sealing region and the active region. An ion exchange membrane is interposed between at least a portion of the fluid distribution layers, and a quantity of electrocatalyst is interposed between at least a portion of each of the fluid distribution layers and at least a portion of the membrane, thereby defining the active region. Melt-bonding the thermoplastic and/or other polymeric material in the sealing region renders the at least one fluid distribution layer substantially fluid impermeable in a direction parallel to the major planar surfaces. This approach reduces or eliminates the need for separate gaskets or sealing components and integrates several functions, such as sealing, fluid distribution, and current collection in a single layer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/384,531, filed on Aug. 27, 1999, entitled “ElectrochemicalCell With Fluid Distribution Layer Having Integral Sealing Capability”.The '531 application is, in turn, a continuation-in-part of U.S. patentapplication Ser. No. 09/309,677, filed on May 11, 1999, also entitled“Electrochemical Cell With Fluid Distribution Layer Having IntegralSealing Capability”. The '677 application is, in turn, a continuation ofU.S. patent application Ser. No. 08/846,653, filed on May 1, 1997, alsoentitled “Electrochemical Cell With Fluid Distribution Layer HavingIntegral Sealing Capability”, now U.S. Pat. No. 5,976,726 issued Nov. 2,1999. Each of the '531 and '653 applications is hereby incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to a fuel cell with a fluid distributionlayer having integral sealing capability.

BACKGROUND OF THE INVENTION

[0003] Electrochemical fuel cells convert fuel and oxidant toelectricity and reaction product. Solid polymer fuel cells generallyemploy a membrane electrode assembly (“MEA”) comprising a solid polymerelectrolyte or ion exchange membrane disposed between two fluiddistribution (electrode substrate) layers formed of electricallyconductive sheet material. The fluid distribution layer has a porousstructure across at least a portion of its surface area, which rendersit permeable to fluid reactants and products in the fuel cell. Theelectrochemically active region of the MEA also includes a quantity ofelectrocatalyst, typically disposed in a layer at each membrane/fluiddistribution layer interface, to induce the desired electrochemicalreaction in the fuel cell. The electrodes thus formed are electricallycoupled to provide a path for conducting electrons between theelectrodes through an external load.

[0004] At the anode, the fluid fuel stream moves through the porousportion of the anode fluid distribution layer and is oxidized at theanode electrocatalyst. At the cathode, the fluid oxidant stream movesthrough the porous portion of the cathode fluid distribution layer andis reduced at the cathode electrocatalyst.

[0005] In fuel cells employing hydrogen as the fuel and oxygen as theoxidant, the catalyzed reaction at the anode produces hydrogen cations(protons) from the fuel supply. The ion exchange membrane facilitatesthe migration of protons from the anode to the cathode. In addition toconducting protons, the membrane isolates the hydrogen-containing fuelstream from the oxygen-containing oxidant stream. At the cathodeelectrocatalyst layer, oxygen reacts with the protons that have crossedthe membrane to form water as the reaction product. The anode andcathode reactions in hydrogen/oxygen fuel cells are shown in thefollowing equations:

Anode reaction: H₂→2H⁺+2e ⁻

Cathode reaction: 1/2O₂+2H⁺+2e ⁻H₂O

[0006] In fuel cells employing methanol as the fuel supplied to theanode (so-called “direct methanol” fuel cells) and an oxygen-containingstream, such as air (or substantially pure oxygen) as the oxidantsupplied to the cathode, the methanol is oxidized at the anode toproduce protons and carbon dioxide. Typically, the methanol is suppliedto the anode as an aqueous solution or as a vapor. The protons migratethrough the ion exchange membrane from the anode to the cathode, and atthe cathode electrocatalyst layer, oxygen reacts with the protons toform water. The anode and cathode reactions in this type of directmethanol fuel cell are shown in the following equations:

Anode reaction: CH₃OH+H₂O→6H⁺+CO₂+6e ⁻

Cathode reaction: 3/2O₂+6H⁺+6e ⁻→3H₂O

[0007] In fuel cells, the MEA is typically interposed between twoseparator plates or fluid flow field plates (anode and cathode plates).The plates typically act as current collectors, provide support to theMEA, and prevent mixing of the fuel and oxidant streams in adjacent fuelcells, thus, they are typically electrically conductive andsubstantially fluid impermeable. Fluid flow field plates typically havechannels, grooves or passages formed therein to provide means for accessof the fuel and oxidant streams to the surfaces of the porous anode andcathode layers, respectively.

[0008] Two or more fuel cells can be connected together, generally inseries but sometimes in parallel, to increase the overall power outputof the assembly. In series arrangements, one side of a given plateserves as an anode plate for one cell and the other side of the platecan serve as the cathode plate for the adjacent cell, hence the platesare sometimes referred to as bipolar plates. Such a series connectedmultiple fuel cell arrangement is referred to as a fuel cell stack. Thestack typically includes manifolds and inlet ports for directing thefuel and the oxidant to the anode and cathode fluid distribution layers,respectively. The stack also usually includes a manifold and inlet portfor directing the coolant fluid to interior channels within the stack.The stack also generally includes exhaust manifolds and outlet ports forexpelling the unreacted fuel and oxidant streams, as well as an exhaustmanifold and outlet port for the coolant fluid exiting the stack.

[0009] The fluid distribution layer in fuel cells has several functions,typically including:

[0010] (1) to provide access of the fluid reactants to theelectrocatalyst;

[0011] (2) to provide a pathway for removal of fluid reaction product(for example, water in hydrogen/oxygen fuel cells and water and carbonmonoxide in direct methanol fuel cells);

[0012] (3) to serve as an electronic conductor between theelectrocatalyst layer and the adjacent separator or flow field plate;

[0013] (4) to serve as a thermal conductor between the electrocatalystlayer and the adjacent separator or flow field plate;

[0014] (5) to provide mechanical support for the electrocatalyst layer;

[0015] (6) to provide mechanical support and dimensional stability forthe ion exchange membrane.

[0016] The fluid distribution layer is electrically conductive across atleast a portion of its surface area to provide an electricallyconductive path between the electrocatalyst reactive sites and thecurrent collectors. Materials that have been employed in fluiddistribution layers in solid polymer fuel cells include:

[0017] (a) carbon fiber paper;

[0018] (b) woven and non-woven carbon fabric optionally filled withelectrically conductive filler such as carbon particles and a binder;

[0019] (c) metal mesh or gauze - optionally filled with electricallyconductive filler such as carbon particles and a binder;

[0020] (d) polymeric mesh or gauze, such as polytetrafluoroethylenemesh, rendered electrically conductive, for example, by filling withelectrically conductive filler such as carbon particles and a binder.

[0021] (e) microporous polymeric film, such as microporouspolytetrafluoroethylene, rendered electrically conductive, for example,by filling with electrically conductive filler such as carbon particlesand a binder.

[0022] Thus, fluid distribution layers typically comprise preformedsheet materials that are electrically conductive and fluid permeable inthe region corresponding to the electrochemically active region of thefuel cell.

[0023] Conventional methods of sealing around MEAs within fuel cellsinclude framing the MEA with a resilient fluid impermeable gasket,placing preformed seal assemblies in channels in the fluid distributionlayer and/or separator plate, or molding seal assemblies within thefluid distribution layer or separator plate, circumscribing theelectrochemical active region and any fluid manifold openings. Examplesof such conventional methods are disclosed in U.S. Pat. Nos. 5,176,966and 5,284,718. Disadvantages of these conventional approaches includedifficulty in assembling the sealing mechanism, difficulty in supportingnarrow seal assemblies within the fluid distribution layer, localizedand uneven mechanical stresses applied to the membrane and sealassemblies, and seal deformation and degradation over the lifetime ofthe fuel cell stack.

[0024] Such gaskets and seals, which are separate components introducedin additional processing or assembly steps, add complexity and expenseto the manufacture of fuel cell stacks.

SUMMARY OF THE INVENTION

[0025] The invention includes a fuel cell with a fluid distributionlayer having integral sealing capability and a method for effectingsealing. The fuel cell comprises:

[0026] (a) a pair of substantially fluid impermeable separator plates;

[0027] (b) a pair of fluid distribution layers interposed between theseparator plates, each of the fluid distribution layers having two majorplanar surfaces, at least one of the fluid distribution layerscomprising a sealing region and an electrically conductive, fluidpermeable active region, the at least one fluid distribution layercomprising polymeric material extending into each of the sealing regionand the active region;

[0028] (c) an ion exchange membrane interposed between at least aportion of the fluid distribution layers;

[0029] (d) a quantity of electrocatalyst interposed between at least aportion of each of the fluid distribution layers and at least a portionof the membrane, thereby defining the active region.

[0030] The polymeric material is melt-bonded in the sealing region,thereby rendering the at least one fluid distribution layersubstantially fluid impermeable in a direction parallel to the majorplanar surfaces, in the sealing region. Thus, the polymeric materialincluded in the at least one fluid distribution layer has intrinsicsealing capability.

[0031] The polymeric material included in the at least one fluiddistribution layer may be melt-bonded to the adjacent separator plate.

[0032] In a preferred fuel cell, each of the fluid distribution layerscomprises a sealing region and an electrically conductive, fluidpermeable active region, and each of the fluid distribution layerscomprises polymeric material extending into each of the sealing regionand the active region.

[0033] In preferred embodiments the membrane superposes at least aportion of the sealing region. Advantageously, therefore, the polymericmaterial in the sealing region of the fluid distribution layer may bemelt-bonded to the ion exchange membrane.

[0034] In preferred embodiments, the polymeric material comprises apolyolefin material, such as, for example polyethylene or polypropylene.

[0035] The fluid distribution layer may be electrically insulating inthe sealing region.

[0036] The polymeric material may be a preformed sheet. In a firstembodiment of a fuel cell, the preformed sheet is a mesh, which mayoptionally contain an electrically conductive filler at least in theactive region. The term mesh as used herein includes woven meshes andexpanded mesh materials. In a second embodiment of a fuel cell, thepreformed sheet is a microporous sheet material.

[0037] Alternatively, the polymeric material (before melt-bonding) maycomprise particulates dispersed throughout the fluid distribution layer.In some embodiments, the particulates may be or include fibers.

[0038] In any of the embodiments described above, at least one of thefluid distribution layers may comprise at least one channel, fordirecting a fluid reactant stream, formed in at least one of the majorplanar surfaces thereof. The at least one channel preferably traversesthe active region.

[0039] In any of the embodiments described above, at least one of theseparator layers may comprise at least one channel formed in a majorsurface thereof facing a fluid distribution layer, for directing a fluidreactant stream in contact with the layer.

[0040] In any of the embodiments described above, a fluid distributionlayer may comprise one or more layers of material.

[0041] In any of the embodiments described above, a fluid distributionlayer may comprise an electrically conductive filler in the activeregion. Preferred electrically conductive fillers comprise a binder andelectrically conductive particles, such as, carbon particles and/orboron carbide particles. The electrically conductive filler may comprisea catalyst and/or an ionomer.

[0042] In any of the above embodiments, the sealing region may have atleast one fluid manifold opening formed therein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043]FIG. 1 is an exploded sectional view of a conventional (prior art)solid polymer fuel cell showing an MEA interposed between two flow fieldplates.

[0044]FIG. 2A is an exploded sectional view, in the direction of arrowsA-A in FIG. 2B, of a fuel cell that includes a pair of fluid flow fieldplates and a pair of fluid distribution layers with integral sealingcapability. The fluid distribution layers include a polymeric mesh sheetmaterial that has been melt-bonded in the sealing region. FIG. 2B is anexploded isometric view of a portion of the fuel cell of FIG. 2A.

[0045]FIG. 3A is an exploded sectional view, in the direction of arrowsB-B in FIG. 3B, of an electrochemical fuel cell which includes a pair offluid flow field plates and a pair of fluid distribution layers withintegral sealing capability. The fluid distribution layers include asubstantially fluid impermeable sheet material having plurality ofperforations formed in the electrochemically active region thereof. FIG.3B is an exploded isometric view of a portion of the fuel cell of FIG.3A.

[0046]FIG. 4A is an exploded sectional view, in the direction of arrowsC-C in FIG. 4B, of an electrochemical fuel cell which includes a pair ofseparator plates and a pair of fluid distribution layers with integralsealing capability. The fluid distribution layers include asubstantially fluid impermeable sheet material having plurality ofperforations in the electrochemically active region thereof, and fluidflow channels formed in a major surface thereof. FIG. 4B is an explodedisometric view of a portion of the fuel cell of FIG. 4A.

[0047]FIG. 5 is a schematic diagram illustrating a fabrication processsuitable for manufacture of fuel cells with fluid distribution layerswith integral sealing capability.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

[0048]FIG. 1 illustrates a typical (prior art) solid polymer fuel cell10. Fuel cell 10 includes an MEA 12 including an ion exchange membrane14 interposed between two electrodes, namely, an anode 16 and a cathode17. Anode 16 includes a porous electrically conductive fluiddistribution layer 18. A thin layer of electrocatalyst 20 is disposed atthe interface with the membrane 14, thereby defining anelectrochemically active region of fluid distribution layer 18. Cathode17 includes a porous electrically conductive fluid distribution layer19. A thin layer of electrocatalyst 21 is disposed at the interface withthe membrane 14, thereby defining an electrochemically active region offluid distribution layer 19. The MEA is interposed between anode flowfield plate 22 and cathode flow field plate 24. Anode flow field plate22 has at least one fuel flow channel 23 formed in its surface facingthe anode fluid distribution layer 18. Cathode flow field plate 24 hasat least one oxidant flow channel 25 formed in its surface facing thecathode fluid distribution layer 19. When assembled against thecooperating surfaces of the fluid distribution layers 18 and 19,channels 23 and 25 form reactant flow field passages for the fuel andoxidant, respectively. Membrane electrode assembly 12 also includespreformed gaskets 26 placed within channels 27, which extend through thethickness of the fluid distribution layers 18 and 19. When the fuel cell10 is assembled and compressed, by urging plates 22 and 24 towards eachother, the gaskets 26 cooperate with the plates 22, 24 and the membrane14 to form a seal circumscribing the electrochemically active region ofeach fluid distribution layer 18, 19.

[0049]FIG. 2A is an exploded sectional view of a fuel cell 210, aportion of which is shown in FIG. 2B in an exploded isometric view. Fuelcell 210 includes a membrane electrode assembly 212, which includes anion exchange membrane 214 interposed between a pair of fluiddistribution layers 218 and 219. A quantity of electrocatalyst isdisposed in a layer 220, 221 at the interface between each fluiddistribution layer 218, 219 and membrane 214 in the electrochemicallyactive region 230 of the fluid distribution layers 218, 219. Thecatalyst may be applied to the membrane or to the fluid distributionlayer. The MEA 212 is interposed between a pair of flow field plates 222and 224. Each plate 222, 224 has an open-faced channel 223, 225 formedin its surface facing the corresponding fluid distribution layer 218,219, respectively, and traversing a portion of each plate thatsuperposes the electrochemically active region 230. When assembledagainst the cooperating surfaces of the fluid distribution layers 218and 219, channels 223 and 225 form reactant flow field passages for thefuel and oxidant, respectively.

[0050] Fluid distribution layers 218, 219 each have a sealing region240. In the illustrated embodiment, ion exchange membrane 214 superposessealing region 240 and may be melt-bonded thereto. In theelectrochemically active region 230, the fluid distribution layers 218,219 are electrically conductive and fluid permeable, to permit thepassage of reactant fluid between the two major planar surfaces thereofto access the electrocatalyst layer 220, 221 respectively. In theembodiment illustrated in FIGS. 2A and 2B, fluid distribution layersinclude an electrically insulating preformed polymeric mesh sheetmaterial 250 extending into each of the active and sealing regions 230,240, respectively. The fluid distribution layer is rendered electricallyconductive in the active region 230, for example, it may contain anelectrically conductive filler, at least in the region 230. Polymericmesh sheet material 250 is melt-bonded at locations 245 in the sealingregion 240 thereby rendering the fluid distribution layers substantiallyfluid impermeable in a direction parallel to their major planarsurfaces. Further, polymeric mesh sheet material 250 is melt-bonded toion exchange membrane 214 at locations 245 thereby also effecting a sealbetween fluid distribution layers 218, 219 and membrane 214. Themelt-bonding within mesh sheet material 250 at locations 245 and themelt-bonding of mesh sheet material 250 to membrane 214 may desirably beaccomplished in one step. A suitable melt-bond may be obtained using aconventional technique appropriate for the joining of thermoplasticsand/or other polymeric materials generally, such as heat bonding orultrasonic welding. Where appropriate, solvent bonding may also beemployed (for example, where a solvent is used to dissolve the polymericsheet material after which the solvent is removed, leaving a melt-bondedpolymeric seal). Seals between the melt-bonded membrane electrodeassembly 212 and plates 222, 224 are effected by compression of thefluid distribution layers 218, 219 in the sealing region 240 betweenplates 222, 224. Thus, complete sealing around the periphery of theactive region 230, is accomplished partly by melt-bonding of thethermoplastic and/or other polymeric material, and partly bycompression. Suitable mesh materials include expanded polyolefinmaterials, such as expanded polypropylene or polyethylene.

[0051] As shown in FIG. 2B, each of membrane 214, fluid distributionlayer 219, reactant flow field plate 224, has a plurality of openings260 formed therein, which align when assembled to form manifolds fordirecting inlet and outlet fluid streams through fuel cell 210. Forexample, oxidant fluid flow field channel 225 extends between oxidantinlet manifold opening 260 a and oxidant outlet manifold 260 b formed inplate 224. The fluid manifold openings 260 in fluid distribution layers218, 219 are formed in sealing region 240. Openings, 260, need notnecessarily be formed in the mesh material of the fluid distributionlayer, as the fluid passing through the manifold can generally readilypass through the mesh material. Melt-bonded locations 245 appear betweenactive region 230 and openings 260.

[0052] In FIG. 2A, other polymeric preformed sheets (for example,suitable microporous films) may be employed in the fluid distributionlayers 218, 219 instead of the expanded polymeric mesh sheet material250. Further, in principle, polymeric particulate filled fluiddistribution layers might also be sealed in this way. Thus, polymericparticulates (for example, plastic fibers) dispersed throughout thefluid distribution layer may be employed instead of a mesh.

[0053] In the embodiment of FIG. 2A, melt-bonding of the fluiddistribution layers to the membrane is preferred since this provides aseal at the fluid distribution layer/membrane interface and may resultin simpler overall manufacture of an MEA. However, this interfacial sealmay instead be effected by compression where desired (for instance ifthe membrane and polymeric material in the fluid distribution layer arenot suitably compatible).

[0054]FIG. 3A is an exploded sectional view of an electrochemical fuelcell 310, a portion of which is shown in FIG. 3B in an explodedisometric view. Again, fuel cell 310 includes a membrane electrodeassembly 312, including an ion exchange membrane 314 interposed betweena pair of fluid distribution layers 318 and 319, with a quantity ofelectrocatalyst disposed in a layer 320, 321 at the interface betweeneach fluid distribution layer 318, 319 and membrane 314 in theelectrochemically active region 330 of the fluid distribution layers318, 319. The MEA 312 is interposed between a pair of flow field plates322 and 324, each plate having an open-faced channel 323, 325 formed inits surface facing the corresponding fluid distribution layer 318, 319,respectively, as described for FIGS. 2A and 2B above.

[0055] Fluid distribution layers 318, 319 each have a sealing region340. In the illustrated embodiment, ion exchange membrane 314 superposesonly a portion of the sealing region 340 circumscribing the activeregion 330. The membrane 314 does not superpose entire sealing region340. In the electrochemically active region 330, the fluid distributionlayers 318, 319 are electrically conductive and fluid permeable. In theembodiment illustrated in FIGS. 3A and 3B, fluid distribution layersinclude substantially fluid impermeable sheet material 350 extendinginto each of the active and sealing regions 330, 340, respectively. Thesheet material 350 is perforated at least in the electrochemicallyactive region, rendering it fluid permeable, to permit the passage ofreactant fluid between the two major planar surfaces thereof for accessto the electrocatalyst layer 320, 321 respectively. In the illustratedembodiment, the substantially fluid impermeable sheet material 350 isformed from an electrically insulating polymeric material such aspolytetrafluoroethylene or an elastomer such as Santoprene brand rubberavailable through Monsanto Company. As the sheet material 350 iselectrically insulating, the fluid distribution layer is renderedelectrically conductive in the active region 330. For example, theperforations 352 may contain an electrically conductive filler 354.Compression of sheet material 350 in fluid distribution layers 318, 319between membrane 314 and plates 322, 324 respectively, renders the fluiddistribution layers substantially fluid impermeable in a directionparallel to their major planar surfaces in the sealing region 340, byvirtue of the fluid impermeability of the sheet material 350 whichextends into the sealing region 340.

[0056] As shown in FIG. 3B, each of the fluid distribution layers 318,319, and reactant flow field plates 322, 324, has a plurality ofopenings 360 formed therein, which align when assembled to formmanifolds for directing inlet and outlet fluid streams through fuel cell310, as described above. For example, oxidant fluid flow field channel325 extends between oxidant inlet manifold opening 360 a and oxidantoutlet manifold 360 b formed in plate 324. The two fluid distributionlayers 318, 319 and the reactant flow field plates 322, 324 cooperate toform a seal circumscribing the manifold openings 360. Whereas sealingaround the periphery of the active region 340 in the embodiment of FIGS.3A and 3B, is accomplished by utilizing the intrinsic sealing capabilityof the sheet material 350 when it is interposed and compressed betweenthe plates 322, 324 and the membrane 314. If the fluid distributionlayers 318, 319 are electrically conductive in sealing region 340 andmembrane 314 does not superpose the entire sealing region 340, anelectrical insulator would need to be interposed between layers 318, 319to prevent short circuiting.

[0057]FIG. 4A is an exploded sectional view of an electrochemical fuelcell 410, a portion of which is shown in FIG. 4B in an explodedisometric view. Fuel cell 410 is very similar to fuel cell 310 of FIGS.3A and 3B, again including a membrane electrode assembly 412, includingan ion exchange membrane 414 interposed between a pair of fluiddistribution layers 418, 419, with electrocatalyst-containing layers420, 421 defining the electrochemically active region 430 of the fluiddistribution layers 418, 419. The MEA 412 is interposed between a pairof separator plates 422 and 424.

[0058] Fluid distribution layers 418, 419 each have a sealing region440. In the illustrated embodiment, ion exchange membrane 414 superposessealing region 440. In the electrochemically active region 430, thefluid distribution layers 418, 419 are electrically conductive and fluidpermeable. In the embodiment illustrated in FIGS. 4A and 4B, fluiddistribution layers include substantially fluid impermeable sheetmaterial 450 extending into each of the active and sealing regions 430,440, respectively. The sheet material 450 is perforated at least in theelectrochemically active region, rendering it fluid permeable, to permitthe passage of reactant fluid between the two major planar surfacesthereof for access to the electrocatalyst layer 420, 421 respectively.In the illustrated embodiment, the substantially fluid impermeable sheetmaterial 450 is formed from an electrically conductive material such asgraphite foil, carbon resin or a metal. The perforations 452 preferablycontain an electrically conductive filler 454.

[0059] In the illustrated embodiment, each fluid distribution layer 418,419 has an open-faced channel 423, 425 formed in its surface facing thecorresponding separator plate 422, 424, respectively, and traversing theelectrochemically active region 430. When assembled against thecooperating surfaces of the plates 422 and 424, channels 423 and 425form reactant flow field passages for the fuel and oxidant,respectively.

[0060] An embodiment such as the one illustrated in FIGS. 4A and 4Bintegrates several functions including sealing, fluid distributionincluding provision of a flow field, and current collection, in a singlelayer or component.

[0061] Compression of sheet material 450 in fluid distribution layers418, 419 between membrane 414 and plates 422, 424, respectively, rendersthe fluid distribution layers 418, 419 substantially fluid impermeablein a direction parallel to their major planar surfaces in the sealingregion 440, by virtue of the fluid impermeability of the sheet material450 which extends into the sealing region 440.

[0062] As shown in FIG. 4B, each of the membrane 414, fluid distributionlayers 418, 419, reactant flow field plates 422, 424, has a plurality ofopenings 460 formed therein, which align when assembled to formmanifolds for directing inlet and outlet fluid streams through fuel cell410, as described above.

[0063] A wide variety of fabrication processes may be used tomanufacture and assemble fuel cells of the present design. The design isbelieved to be suited for high throughput manufacturing processes, suchas the reel-to-reel type process disclosed in the aforementioned U.S.patent application Ser. No. 08/846,653 incorporated herein by reference.Such a reel-to-reel process may consolidate several webs consisting ofthe fluid distribution layers, a catalyzed membrane, and a separatorlayer. The consolidation step could include a thermal lamination(thereby effecting the melt-bonding between the fluid distributionlayers and the membrane) and a pressure bonding process.

[0064]FIG. 5 is a schematic diagram illustrating a possible fabricationapproach for a fuel cell similar to that illustrated in FIGS. 4A and 4B.FIG. 5 shows schematically the preparation of a fluid distributionlayers 518, and the consolidation of two such layers 518, 519 with acatalyzed membrane 514 and a separator layer 522, in a reel-to-reel typeprocess. For example, fluid distribution layers 518 are formed byselectively perforating a substantially fluid impermeable preformedsheet material 550 in the active region, in a perforation step 580. Thesheet material could, for example, be graphite foil. In a subsequentstep 585, the perforations are at least partially filled with anelectrically conductive filler, such as carbon particles and a polymericbinder. A layer of conductive filler may also be deposited on one orboth major surfaces of the perforated sheet material 550. Reactant flowfield channels 523 may be formed in one or both major surfaces of thefluid distribution layer in step 590, for example, by embossing. Amulti-layer fuel cell assembly 510 may be formed by bringing together,in a consolidation step 595, two fluid distribution layers 518, 519,with an ion exchange membrane 514, and a substantially fluid impermeableseparator layer 522. The consolidation step could include a thermallamination and/or pressure bonding process. The ion exchange membrane514 has a electrocatalyst-containing layer on a portion of both of itsmajor surfaces, defining the electrochemically active region.Alternatively, the electrocatalyst could be deposited on the fluiddistribution layers 518, 519 prior to consolidation step 595. Theassemblies may then optionally be cut into single cell units, andlayered to form a fuel cell stack, wherein separator layers 522 willserve as bipolar plates. FIG. 5 illustrates how the present fuel celldesign with fluid distribution layers with integral seal capability, issuitable for fabrication via a continuous, high throughput manufacturingprocess, with little material wastage and few individual components andprocessing steps.

[0065] The practical advantages of the present fuel cell with a fluiddistribution layer having integral sealing capability is the combinationof the sealing and fluid distribution functions into one fluiddistribution layer, thereby reducing cost, simplifying the components,and improving their reliability. This approach reduces or eliminates theneed for separate sealing components in a fuel cell assembly.

[0066] In all of the above embodiments, the fuel cell may includeadditional layers of material interposed between those shown, or thecomponents shown may be multi-layer structures. Such additional layersmay or may not superpose both the electrochemically active region andthe sealing region. The separator plates may have optionally have raisedsealing ridges projecting from the major surfaces thereof in the sealingregion. In a fuel cell assembly under compression, the sealing ridgeswill compress the fluid distribution layer.

[0067] Those in the art will appreciate that the general principlesdisclosed in the preceding can be expected to apply to both gas andliquid feed fuel cells, for example, gaseous hydrogen/air solid polymerfuel cells and liquid methanol/air or “direct methanol” solid polymerfuel cells. However, it is expected that fewer polymers will be suitablefor use in the latter since a suitable polymer would have to becompatible with liquid methanol.

[0068] While particular elements, embodiments and applications of thepresent invention have been shown and described, it will be understood,of course, that the invention is not limited thereto since modificationsmay be made by those skilled in the art, particularly in light of theforegoing teachings. It is therefore contemplated by the appended claimsto cover such modifications as incorporate those features that comewithin the scope of the invention.

What is claimed is:
 1. A method of sealing at least one of a pair offluid distribution layers in a fuel cell, the fuel cell comprising: (a)a pair of substantially fluid impermeable separator plates havingassociated therewith a compressive mechanism for urging said platestowards each other; (b) a pair of fluid distribution layers interposedbetween said separator plates, each of said fluid distribution layershaving two major planar surfaces, at least one of said fluiddistribution layers comprising a sealing region and an electricallyconductive, fluid permeable active region, said at least one fluiddistribution layer comprising a preformed sheet material extending intoeach of said sealing region and said active region; (c) an ion exchangemembrane interposed between at least a portion of said fluiddistribution layers; (d) a quantity of electrocatalyst interposedbetween at least a portion of each of said fluid distribution layers andat least a portion of said membrane, thereby defining said activeregion; the method comprising compressing said preformed sheet materialby urging said pair of plates towards each other, whereby said at leastone fluid distribution layer is rendered substantially fluid impermeablein a direction parallel to said major planar surfaces, in said sealingregion.
 2. The method of claim 1 wherein said at least one of said fluiddistribution layers is both of said pair of fluid distribution layers.3. The method of claim 1 wherein said membrane superposes at least aportion of said sealing region.
 4. The method of claim 1 furthercomprising electrically insulating said at least one fluid distributionlayer in said sealing region.
 5. The method of claim 1 wherein saidpreformed sheet material is a mesh.
 6. The method of claim 5 whereinsaid mesh is electrically conductive.
 7. The method of claim 6 whereinsaid mesh contains an electrically conductive filler at least in saidactive region.
 8. The method of claim 6 wherein said mesh consistsessentially of a metal.
 9. The method of claim 8 wherein said metal isselected from the group consisting of nickel, stainless steel, niobiumand titanium.
 10. The method of claim 5 wherein said mesh is anelectrical insulator, said mesh containing an electrically conductivefiller at least in said active region.
 11. The method of claim 10wherein said mesh consists essentially of a polymeric material.
 12. Themethod of claim 11 wherein said polymeric material is selected from thegroup consisting polyethylene, polypropylene andpolytetrafluoroethylene.
 13. The method of claim 1 wherein saidpreformed sheet material is a substantially fluid impermeable sheetmaterial, the method further comprising rendering said sheet materialfluid permeable in said active region.
 14. The method of claim 13wherein said substantially fluid impermeable sheet material is renderedfluid permeable by perforating said sheet material at least in saidactive region.
 15. The method of claim 14 wherein said substantiallyfluid impermeable sheet material is electrically conductive.
 16. Themethod of claim 15 wherein said substantially fluid impermeable sheetmaterial is graphite foil.
 17. The method of claim 15 wherein said atleast one fluid distribution layer comprises an electrically conductivefiller within perforations in said perforated active region.
 18. Themethod of claim 14 wherein said substantially fluid impermeable sheetmaterial is an electrical insulator, and said at least one fluiddistribution layer comprises an electrically conductive filler withinperforations in said perforated active region.
 19. The method of claim18 wherein said substantially fluid impermeable sheet material consistsessentially of a polymeric material.
 20. The method of claim 1 furthercomprising forming at least one channel in at least one of said majorplanar surfaces of said at least one fluid distribution layer, said atleast one channel traversing said active region and adapted to direct afluid reactant stream therein.
 21. The method of claim 1 furthercomprising forming at least one channel in at least one of said majorplanar surfaces of said at least one fluid distribution layer, said atleast one channel adapted to direct a fluid reactant stream in contactwith said layer.
 22. A method of sealing at least one of a pair of fluiddistribution layers in a fuel cell, the fuel cell comprising: (a) a pairof substantially fluid impermeable separator plates; (b) a pair of fluiddistribution layers interposed between said separator plates, each ofsaid fluid distribution layers having two major planar surfaces, atleast one of said fluid distribution layers comprising a sealing regionand an electrically conductive, fluid permeable active region, said atleast one fluid distribution layer comprising a porous electricallyinsulating sheet material extending into each of said active region andsaid sealing region; (c) an ion exchange membrane interposed between atleast a portion of said fluid distribution layers; (d) a quantity ofelectrocatalyst interposed between at least a portion of each of saidfluid distribution layers and at least a portion of said membrane,thereby defining said active region; the method comprising disposing anelectrically conductive filler in said active region and a sealingfiller in said sealing region, whereby said fluid distribution layer isrendered substantially fluid impermeable in said sealing region.
 23. Themethod of claim 22 wherein said porous electrically insulating sheetmaterial consists essentially of a polymeric material.
 24. The method ofclaim 23 wherein said polymeric material is microporous.
 25. The methodof claim 23 wherein said polymeric material is selected from the groupconsisting polyethylene, polypropylene and polytetrafluoroethylene 26.The method of claim 22 wherein said porous electrically insulating sheetmaterial is a mesh.
 27. The method of claim 22 wherein said porouselectrically insulating sheet material is glass fiber mat.
 28. Themethod of claim 22 wherein said sealing filler comprises a flowprocessible material.
 29. The method of claim 28 wherein said flowprocessible material is an elastomer.
 30. The method of claim 29 whereinsaid elastomeric flow processible material is silicon rubber.